Circular knitting machines are often used for production of many different types of fabric. One type of fabric that is produced on such knitting machines is fleece fabric made up of fleece yarns, tie-in yarns and knit-in yarns. Since such knitting machines are usually employed in commercial knitting mills, it is often desirable that the machines be operated at a speed that is as high as possible for producing quality fabric without resulting in excessive machine breakage or down time, and without causing undesired fabric defects. This practice maximizes the amount of quality fabric that may be produced in a given amount of time, thus improving the profitability of the machine.
Heretofore, the operation of knitting machines has been restricted by limitations in the design of certain internal components of the machines which must be reciprocated at high speeds, and thus under conditions of high acceleration and wear, to produce fabric. A sinker is one such part that must be reciprocated quickly in the machine during operation. Likewise, the knitting needles which act in concert with the sinkers in the machine must be reciprocated quickly, and latches on the needles opened and closed rapidly, thus also leading to speed limitations. Both of these components are generally moved by cams having undulating tracks which are engaged by butts that are fixedly attached to the sinkers and needles.
One problematic aspect of the operation of knitting machines is the distance over which the needle must be retracted in order to roll over, or close, the latch of the needle during the knitting cycle. "Typically, the latch is rolled over by a previously knit loop of yarn that is positioned around the needle shaft. The position of this yarn loop is generally controlled by a knitting platform and/or throat of the sinker. Retraction of the needle past the knitting platform causes the loop to slide along the needle shaft and to move over the latch, thus rolling the latch over.
During knitting, it is desirable to close the arch as quickly as possible to prevent fabric defects such as dropped stitches, commonly known as "birds eye" or "cat face," which may result when torque in the yarn causes the yarn to twist out of the open hook of the needle in particular, dropped stitches may occur during fleece knitting when a tie-in yarn, which is typically looped loosely across the needle, "squirms" out of the needle hook before the latch is closed. Faster closing of the latch, therefore, reduces the occurrence of such fabric defects when the knitting machine is operated. Prior knitting machines, and the sinkers and needles installed in them, have not adequately solved the occurrence of dropped stitches.
Also, for the latch roll over to be accomplished properly, it is necessary that the latch length be selected so that the latch reaches the location of the previously knitted loop on the knitting platform at the proper time as the needle is retracted. This condition is due to the necessity that the needle must be retracted a predetermined distance, which takes time, in order for the latch to be rolled over. Therefore, the combination of the latch length and the position of the knitting platform may affect the speed of the knitting machine.
For example, the model 4FST fleece knitting machine, which was manufactured in the early 1980's by the Vanguard Supreme Division of Monarch Knitting Machinery Corporation, Monroe, N.C., used a sinker having a linear knitting platform for controlling the position of previously knitted loops of fabric. In this machine, a latch length of about 9.5 mm was used, which permitted an operating speed factor of about 630, which equals about 21 revolutions per minute for a thirty inch (30") diameter knitting machine.
In a successive model, the 4SFT/2 fleece knitting machine, which was made and sold by the Vanguard Supreme Division in about 1985, the knitting platform of the sinkers was characterized by two levels. One level of the knitting platform was further removed from the top throat of the sinker, and the other level was positioned closer to the top throat. In this machine, a latch length is 8.0 mm. This development improved operating speeds somewhat, enabling the 4FST/2 machine to be operated at a speed factor of about 720 (i.e., about 24 revolutions per minute for a 30" diameter knitting machine). This division of the knitting platform into two levels permitted the latch length to be shortened somewhat by positioning the yarn loop on the elevated level of the platform closer to the top throat of the sinker; however, the amount by which the single elevated portion of the knitting platform could be removed from the lower knitting platform was limited, as further removal of the two platforms from each other would affect the stitch length of the knitting machine. Also, yarn defects could still result from machine operation, since the yarns could still twist out of the hooks, causing dropped stitches.
Another characteristic of high speed operation of knitting machines is the likelihood of component breakage due to high stresses imparted to the internal parts of the machine, or due to inadvertent introduction of foreign matter into the working parts of the machine that impedes their function. For example, high speed operation of knitting machines requires that the sinkers in the machine reciprocate very quickly. The sinkers are generally caused to reciprocate by cooperation of a butt portion of the sinker with a cam having an undulating track through which the butt moves. This arrangement leads to high acceleration of the sinkers, since the direction of travel of the sinkers is rapidly reversed. Consequently, high stresses are imposed on parts of the sinkers, particularly at the butt, and on other related components of the knitting machine.
Heretofore, breakage of a sinker butt within the closed confines of the knitting machine cam has been prone to cause relatively disastrous results. For example, breakage of one butt in one sinker in known knitting machines is likely to break other butts adjacent to and downstream of a first broken butt. In extreme cases, such breakage may lead to breakage or damage of the knitting machine cams or other components. Such events have therefore frequently necessitated that operation of the machine be stopped for relatively extended time periods so that the machine may be repaired and new components such as sinkers installed. Of course, repair of such damage and replacement of parts may be expensive. Also, the down time necessitated for such repair and replacement activities interferes with the productivity of the knitting machine.
In accordance with the foregoing, one object of the present invention is to provide a sinker for use in a circular knitting machine that will cause the latch of a needle acting in concert with the sinker to be closed more quickly than in prior knitting machines so as to reduce fabric defects such as "birds eye" or "cat face" due to yarn being twisted out of the needle hook due to yarn torque.
Another object of the present invention is to provide a sinker for use in a circular knitting machine which facilitates increased machine operating speeds in conjunction with needles having a desired latch length.
A further object of the present invention is to provide a sinker for use in a circular knitting machine for high speed production of fleece fabric.
Another object of the present invention is to provide a sinker for high speed production of fleece fabric in a circular knitting machine.
Yet another object of the present invention is to provide a sinker for use in high speed production of fleece fabric on a circular knitting machine with knitting needles having short latches.
A still further object of the present invention is to provide a sinker for use in a circular knitting machine that has a butt for reducing the likelihood of damaging other sinkers or components of the knitting machine in the event that the butt is damaged.
A further object of the present invention is to provide a sinker having a butt designed to deform or break partially instead of breaking fully in the event of encountering an obstruction in the sinker cam, so as to reduce the likelihood of damaging other sinkers or components of the knitting machine.
A still further object of the present invention is to provide a sinker for reducing down time of the knitting machine due to broken sinker butts.